JP2023077787A - Wiring circuit board and manufacturing method thereof - Google Patents

Abstract

To provide a wiring circuit board comprising a conduction section having high adhesiveness and high connection reliability, and a manufacturing method thereof.SOLUTION: A wiring circuit board 1 comprises: an insulation layer 2 including a via 20 penetrating in a thickness direction; a first conductor layer 3 disposed on one surface 27 of the insulation layer 2 in the thickness direction; a second conductor layer 4 disposed on another surface 28 of the insulation layer 2 in the thickness direction; and a conduction section 5 which is disposed on an inner side face 25 of the via 20 and electrically connects the first conductor layer 3 and the second conductor layer 4. A length L measured as follows is 1 μm or longer and 10 μm or shorter. In a cross-sectional view, for the length L, a line segment S is drawn, the line segment connecting a first connection point C1 where the one surface 27 of the insulation layer 2 is connected with the inner side face 25 in the thickness direction and a second connection point C2 where the other surface 28 of the insulation layer 2 is connected with the inner side face 25 in the thickness direction. In the cross-sectional view, an outermost position P separated most outside from the line segment S is identified on the inner side face 25. The length L is measured as a shortest distance from the line segment S to the outermost position P.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a printed circuit board and a manufacturing method thereof.

A wired circuit board is known that includes a first conductor layer, an insulating layer, and a second conductor layer in order in the thickness direction (see, for example, Patent Document 1 below). In the printed circuit board described in Patent Document 1, the insulating layer has blind vias. The printed circuit board further includes a conductive portion. The conducting portion is arranged on the inner surface of the insulating layer facing the blind via. In the printed circuit board, the conductive portion electrically connects the first conductor layer and the second conductor layer.

JP 2019-123851 A

In the printed circuit board, high adhesion to the inner surface of the conductive portion is required. In addition, in the printed circuit board, high connection reliability of the conductive portion is required.

However, the printed circuit board described in Patent Document 1 may not satisfy the above requirements.

SUMMARY OF THE INVENTION The present invention provides a printed circuit board having a conductive portion with high adhesion and high connection reliability, and a method for manufacturing the printed circuit board.

The present invention (1) comprises an insulating layer having vias penetrating in the thickness direction, a first conductor layer disposed on one side of the insulating layer in the thickness direction, and a conductor layer on the other side of the insulating layer in the thickness direction. a second conductor layer disposed; and a conductive portion disposed on the inner side surface of the via and electrically connecting the first conductor layer and the second conductor layer, and the length L measured below is , 1 μm or more and 10 μm or less.

Length L: In a cross-sectional view, a first connection point C1 where the one surface and the inner side surface of the insulating layer in the thickness direction are connected, and the other surface and the inner side surface of the insulating layer in the thickness direction are connected. A line segment S connecting the second connection point C2 is drawn. In a cross-sectional view, an outermost position P farthest from the line segment S is specified on the inner surface. A length L is measured as the shortest distance from the line segment S to the outermost position P.

In this printed circuit board, since the length L is 1 μm or more, the adhesion to the inner surface of the conductive portion is excellent based on the high anchor effect to the inner surface of the conductive portion.

In this printed circuit board, since the length L is 10 μm or less, defective formation of the conductive portion is suppressed, so that the connection reliability of the conductive portion to the first conductor layer and the second conductor layer is excellent.

The present invention (2) includes the printed circuit board according to (1), wherein the insulating layer includes a porous insulating layer.

In this printed circuit board, since the insulating layer includes a porous insulating layer, the length L can be ensured to be 1 μm or more.

The present invention (3) includes the printed circuit board according to (1) or (2), wherein the inner surface has a tapered shape when the cross section is viewed macroscopically.

In this wired circuit board, since the inner surface has a tapered shape when the cross section is viewed macroscopically, it is possible to further suppress formation defects of the conductive portions.

The present invention (4) is a method for manufacturing a wired circuit board according to any one of (1) to (3), wherein a laminate comprising a second conductor layer, an insulating layer, and a base conductor layer is provided. irradiating the laminate with a laser from one side in the thickness direction to form vias in the underlying conductor layer and the insulating layer; forming an additional conductor layer on the one side of the laminate; and forming a conductive portion on the inner side surface of the via, wherein the step of forming the via includes a step of irradiating a laser at an energy density of 1 J/cm ² or more and 20 J/cm ² or less. including a method of manufacturing a printed circuit board.

According to this manufacturing method, the step of forming the via includes the step of irradiating the laser with an energy density of 1 J/cm ² or more and 20 J/cm ² or less. L can be controlled to 10 μm or less.

According to the present invention (5), in the step of forming the via, when viewed in the thickness direction, the laser is rotated from the inside toward the outside in the region where the via is formed, according to (4). It includes a method of making the wired circuit board described.

According to this method, the laser is rotated from the inside toward the outside, so that the inner surface can be easily formed into a tapered shape.

The present invention (6) is the wiring circuit according to (4) or (5), wherein in the step of preparing the laminate, the insulating layer includes an adhesive insulating layer and a porous insulating layer in order in the thickness direction. Including the method of manufacturing the substrate.

The printed circuit board and the method for manufacturing the same of the present invention are provided with a conductive portion having high adhesion and high connection reliability.

FIG. 1 is a cross-sectional view of one embodiment of the wired circuit board of the present invention. 2A and 2B are both plan views of the printed circuit board shown in FIG. FIG. 2A shows how the laser is rotated from the inside to the outside in the region where the via is formed. FIG. 2B shows how the laser is rotated from the outside to the inside in the region where the via is formed. FIG. 3 is a cross-sectional view of the inner surface viewed macroscopically. 4A to 4C are manufacturing process diagrams of the printed circuit board shown in FIG. FIG. 4A is a step of preparing a laminate. FIG. 4B is a step of forming vias. FIG. 4C is the step of forming additional conductor layers and conducting portions. FIG. 5 is a cross-sectional view of a first modified example. FIG. 6 is a cross-sectional view of a second modified example. 7 is an image-processed SEM photograph of the inner surface of Example 1. FIG.

1. Wiring circuit board 1
One embodiment of the wired circuit board of the present invention will be described with reference to FIGS. 1 to 4C. As shown in FIG. 1, the printed circuit board 1 has a sheet shape. The printed circuit board 1 has a thickness. The printed circuit board 1 extends in the planar direction. The plane direction is perpendicular to the thickness direction. The printed circuit board 1 includes an insulating layer 2 , a first conductor layer 3 , a second conductor layer 4 , and a conductive portion 5 .

1.2 Insulating layer 2
The insulating layer 2 has a sheet shape. The insulating layer 2 extends in the planar direction. The insulating layer 2 has the same outline shape as the wired circuit board 1 in plan view. The insulating layer 2 has one surface 27 and the other surface 28 facing each other in the thickness direction. Each of the one surface 27 and the other surface 28 is flat. The other surface 28 is parallel to the one surface 27 .

A material for the insulating layer 2 is resin. Examples of resins include polyimide resins, fluororesins, and liquid crystal polymers. Resins include adhesives. Examples of adhesives include acrylic adhesives, epoxy adhesives, and silicone adhesives. These can be used alone or in combination. The thickness of the insulating layer 2 is, for example, 2 μm or more, preferably 5 μm or more, and is, for example, 1,000 μm or less, preferably 500 μm or less.

The insulating layer 2 includes an adhesive insulating layer 21 and a porous insulating layer 22 in order toward one side in the thickness direction. In this embodiment, the insulating layer 2 preferably comprises only the adhesive insulating layer 21 and the porous insulating layer 22 .

1.2.1 Adhesive insulating layer 21
The adhesive insulating layer 21 is the other side portion of the insulating layer 2 in the thickness direction. The adhesive insulating layer 21 forms the other side 28 of the insulating layer 2 . The adhesive insulating layer 21 is dense and not porous. The adhesive insulating layer 21 bonds the porous insulating layer 22 and the second conductor layer 4 together. The material of the adhesive insulating layer 21 is, for example, the adhesive described above. The thickness of the adhesive insulating layer 21 is, for example, 2 μm or more, preferably 5 μm or more, and is, for example, 50 μm or less, preferably 25 μm or less. The ratio of the thickness of the adhesive insulating layer 21 to the thickness of the insulating layer 2 is, for example, 1% or more, preferably 3% or more, and is, for example, 70% or less, preferably 50% or less. The material and physical properties of the adhesive insulating layer 21 are described in JP-A-2020-049905.

1.2.2 Porous insulating layer 22
The porous insulating layer 22 is one side portion of the insulating layer 2 in the thickness direction. Porous insulating layer 22 forms one side 27 of insulating layer 2 . The porous insulating layer 22 is arranged on one side of the adhesive insulating layer 21 in the thickness direction. Specifically, the porous insulating layer 22 is in contact with the entire one surface of the adhesive insulating layer 21 in the thickness direction. The porous insulating layer 22 has many fine pores (pores). The thickness of the porous insulating layer 22 is, for example, 2 μm or more, preferably 5 μm or more, and is, for example, 1,000 μm or less, preferably 500 μm or less. The ratio of the thickness of the porous insulating layer 22 to the thickness of the insulating layer 2 is, for example, 20% or more, preferably 50% or more, and is, for example, 95% or less, preferably 90% or less. The ratio of the thickness of the porous insulating layer 22 to the thickness of the adhesive insulating layer 21 is, for example, 0.5 or more, preferably 1 or more, and is, for example, 50 or less, preferably 20 or less. Materials for the porous insulating layer 22 include the resins described above. The average pore size of the porous insulating layer 22 is, for example, 10 μm or less, and is, for example, 0.1 μm or more. The porosity of the porous insulating layer 22 is, for example, 60% or more, preferably 70% or more, and is, for example, 99% or less, preferably 90% or less. The material and physical properties of the porous insulating layer 22 are described in JP-A-2018-021171 and JP-A-2020-049905.

The insulating layer 2 including the adhesive insulating layer 21 and the porous insulating layer 22 described above is described in JP-A-2020-049905.

1.2.3 Via 20
The insulating layer 2 further comprises vias 20 . One or more vias 20 are provided in the insulating layer 2 . The via 20 penetrates through the insulating layer 2 in the thickness direction. The via 20 also penetrates the first conductor layer 3 . On the other hand, the vias 20 do not penetrate the second conductor layer 4 . The via 20 is visible from one side in the thickness direction and invisible from the other side. Therefore, the via 20 is called a blind via. 2A and 2B, in this embodiment, the via 20 has a substantially circular shape when viewed from one side in the thickness direction. As shown in FIG. 1, insulating layer 2 has an inner surface 25 facing via 20 . The inner surface 25 will be described later.

1.3 First conductor layer 3
The first conductor layer 3 is arranged on one surface of the insulating layer 2 in the thickness direction. The first conductor layer 3 contacts the entire one surface of the insulating layer 2 in the thickness direction. Examples of the material of the first conductor layer 3 include metal, preferably copper. The thickness of the first conductor layer 3 is, for example, 0.1 μm or more, preferably 1 μm or more, and is, for example, 100 μm or less, preferably 50 μm or less. The first conductor layer 3 is described in JP-A-2020-049905.

1.4 Second conductor layer 4
The second conductor layer 4 is arranged on the other side of the insulating layer 2 in the thickness direction. The second conductor layer 4 contacts the entire other surface of the insulating layer 2 in the thickness direction. Furthermore, the second conductor layer 4 closes the lower ends of the vias 20 in the insulating layer 2 . The material of the second conductor layer 4 is, for example, the same as the material of the first conductor layer 3, specifically copper. The thickness of the second conductor layer 4 is, for example, 0.1 μm or more, preferably 1 μm or more, and is, for example, 100 μm or less, preferably 50 μm or less. The second conductor layer 4 is described in JP-A-2020-049905.

1.5 Continuity part 5
The conducting portion 5 is arranged inside the via 20 . Specifically, the conducting portion 5 is arranged on the inner side surface 25 of the insulating layer 2 facing the via 20 . The conducting portion 5 is continuous with a portion of the first conductor layer 3 facing one end of the via 20 in the thickness direction and a peripheral end portion of a portion of the second conductor layer 4 closing the via 20 . That is, the conductive portion 5 is continuous with the first conductor layer 3 and the second conductor layer 4 . Thereby, the conducting portion 5 electrically connects the first conductor layer 3 and the second conductor layer 4 . The conductive portion 5 has a film shape that follows the inner surface 25 . The material of the conductive portion 5 is, for example, the same as the material of the first conductor layer 3, specifically copper.

1.6 Inner surface 25
The inner side surface 25 has, for example, fine unevenness. The uneven shape is formed, for example, by the physical properties of the insulating layer 2 (for example, fine pores in the porous insulating layer 22 ) and the manufacturing method of the wired circuit board 1 . Further, on the inner surface 25, the length L1 measured by the following is 1 μm or more and 10 μm or less.

Length L: In a cross-sectional view, a first connection point C1 where the one surface 27 and the inner side surface 25 of the insulating layer 2 in the thickness direction connect, and a first connection point C1 where the other surface 28 and the inner side surface 25 of the insulating layer 2 in the thickness direction connect. 2 draw a line segment S connecting the connection point C2. The outermost position P farthest from the line segment S is specified on the inner surface 25 in a cross-sectional view. A length L is measured as the shortest distance from the line segment S to the outermost position P.

If the length L1 is less than 1 μm, the anchoring effect on the inner surface 25 of the conductive portion 5 is low, so that the adhesion of the conductive portion 5 to the inner surface 25 is low.

If the length L1 exceeds 10 μm, formation defects of the conductive portion 5 are likely to occur in the manufacturing method described later, and the connection reliability of the conductive portion 5 to the first conductor layer 3 and the second conductor layer 4 is lowered.

The length L1 is preferably 2 μm or more, more preferably 4 μm or more, still more preferably 5 μm or more. If the length L1 is equal to or greater than the above-described lower limit, the anchoring effect of the conductive portion 5 to the inner surface 25 can be enhanced, thereby further improving the adhesion of the conductive portion 5 to the inner surface 25 .

The length L1 is preferably 9 μm or less, more preferably 8 μm or less, even more preferably 7 μm or less. If the length L1 is equal to or less than the upper limit described above, defective formation of the conductive portion 5 is further suppressed in the manufacturing method, and connection reliability of the conductive portion 5 to the first conductor layer 3 and the second conductor layer 4 is further improved. can improve.

The length L1 is adjusted according to the average pore diameter, porosity, and/or laser irradiation conditions (described later) of the porous insulating layer 22 .

In this embodiment, the outermost position P preferably exists in the porous insulating layer 22 .

The cross-sectional view is performed by observing an image-processed SEM photograph, for example, as shown in FIG.

As shown in FIG. 3, the inner surface 25 has a tapered shape when the cross section is viewed macroscopically. "Macroscopically viewed" means that the shape of the inner surface 25 is roughly grasped by smoothing out the unevenness described above. In the tapered shape described above, when the cross section is viewed macroscopically, the opening area gradually increases toward one side in the thickness direction.

1.7 Method for Manufacturing Wired Circuit Board 1 Next, a method for manufacturing the wired circuit board 1 will be described. The method for manufacturing the printed circuit board 1 includes, in order, a step of preparing the laminate 6, a step of forming the vias 20, and a step of forming the conducting portions 5. As shown in FIG.

1.7.1 Step of Preparing Layered Body 6 As shown in FIG. 4A, the layered body 6 includes the second conductor layer 4, the insulating layer 2, and the base conductor layer 31, which are arranged in one direction in the thickness direction. Prepare in order. The insulating layer 2 in the stack 6 does not yet have vias 20 (see FIG. 1). The underlying conductor layer 31 is arranged on one side of the insulating layer 2 in the thickness direction. The underlying conductor layer 31 corresponds to the other side portion of the first conductor layer 3 in the thickness direction. In this embodiment, the base conductor layer 31 is a base for forming an additional conductor layer 32 (see FIG. 4C, which will be described later) by plating. Laminate 6 and its preparation method are described in JP-A-2020-049905.

1.7.2 Step of Forming Via 20 Next, as shown in FIG. 4B, the laminated body 6 is irradiated with a laser from one side in the thickness direction to form the via 20 in the base conductor layer 31 and the insulating layer 2. .

Examples of lasers include YAG lasers and carbon dioxide lasers. The number of laser irradiation steps may be singular or plural, preferably two from the viewpoint of high production efficiency and favorable shape of via 20 . That is, the process of forming the via 20 includes a first irradiation process and a second irradiation process in this order. In both the first irradiation step and the second irradiation step, the laminated body 6 is irradiated with the laser.

The energy density in the first irradiation step is, for example, 1 J/cm ² or more, preferably 10 J/cm ² or more, and is, for example, 20 J/cm ² or less, preferably 18 J/cm ² or less. If the energy density in the first irradiation step is equal to or higher than the above lower limit, the production efficiency can be improved. If the energy density in the first irradiation step is equal to or less than the above upper limit, the length L can be controlled to be equal to or less than the above upper limit, and the via 20 can be tapered.

The energy density in the second irradiation step is, for example, lower than the energy density in the first irradiation step. By making the energy density in the second irradiation step lower than the energy density in the first irradiation step, the insulating layer 2 can be removed while leaving the underlying conductor layer 31.

Specifically, the ratio of the energy density in the second irradiation step to the energy density in the first irradiation step is, for example, 0.01 or more, preferably 0.02 or more, and for example, 0.4 or less, Preferably, it is 0.1 or less. Specifically, the energy density in the second irradiation step is, for example, 0.01 J/cm ² or more and, for example, 0.1 J/cm ² or less.

In the step of forming the via 20, an irradiation method in which the laser is swirled from the inside toward the outside as shown by the arrow in FIG. 2A in the region where the via 20 is formed when viewed in the thickness direction; As indicated by the arrow in FIG. 2B, an irradiation method is used in which the direction is turned from the outside to the inside. The number of turns is plural. Preferably, when viewed in the thickness direction, the laser is swirled from the inside to the outside, as indicated by the arrow in FIG. 2A, within the region where the via 20 is formed. With this irradiation method, the spot with the highest energy in the laser irradiation exists on the wall surface of the via 20 for a long time in the first half of the irradiation time. can be shaped. On the other hand, if the laser is rotated from the outside toward the inside as indicated by the arrow in FIG. The above-described portions are also affected, and the inner side surface 25 may have a shape in which an intermediate portion in the thickness direction bulges outward, as in a first modified example described later.

As shown in FIG. 4B, vias 20 are formed in the underlying conductor layer 31 and the insulating layer 2 by this step. On the other hand, no vias 20 are formed in the second conductor layer 4 .

1.7.3 Step of forming conductive portion 5 Next, as shown in FIG. 25.

The additional conductor layer 32 corresponds to one side portion of the first conductor layer 3 in the thickness direction. An additional conductor layer 32 is added to the underlying conductor layer 31 to form the first conductor layer 3 . In this step, for example, plating or sputtering is performed, preferably plating is performed. Through this process, the additional conductor layer 32 and the conductive portion 5 are formed at the same time. The additional conductor layer 32 is also added to the portion of the second conductor layer 4 that closes the lower end of the via 20 . If the additional conductor layer 32 and the underlying conductor layer 31 are made of the same material, their boundary becomes unclear.

The conductive portion 5 enters the uneven portion of the inner surface 25 and has an anchoring effect on the inner surface 25 of the conductive portion 5 .

2. Advantages of One Embodiment In this wired circuit board 1, since the length L is 1 μm or more, the adhesion of the conducting portion 5 to the inner side surface 25 is excellent based on the high anchor effect to the inner side surface 25 of the conducting portion 5. .

In this printed circuit board 1, since the length L is 10 μm or less, defective formation of the conductive portion 5 is suppressed. Excellent. The malformation of the conductive portion 5 includes cracks and/or voids.

In the wired circuit board 1, the insulating layer 2 includes the porous insulating layer 22, so that the length L can be ensured to be 1 μm or more.

As shown in FIG. 3 , in this wired circuit board 1 , the inner side surface 25 has a tapered shape when viewed macroscopically in cross section, so that formation defects of the conductive portions 5 can be further suppressed.

According to this manufacturing method, the step of forming the via 20 includes the first irradiation step of irradiating the laser with an energy density of 1 J/cm ² or more and 20 J/cm ² or less. The length L at the side surface 25 can be controlled to 10 μm or less.

3. Modified Example In the modified example, the same reference numerals are given to the same members and steps as in the embodiment, and detailed description thereof will be omitted. In addition, the modified example can have the same effects as the one embodiment, unless otherwise specified. Furthermore, one embodiment and its modifications can be combined as appropriate.

3.1 First Modification As shown in FIG. 5, the inner side surface 25 bulges outward at an intermediate portion in the thickness direction when the cross section is viewed macroscopically. Therefore, the via 20 has a substantially pot-like cross-sectional view.

When one embodiment is compared with the first modified example, one embodiment is preferred. As shown in FIG. 3, in one embodiment, the inner side surface 25 has a tapered shape when the cross section is viewed macroscopically. .

3.2 Second Modification As shown in FIG. 6, the insulating layer 2 includes a porous insulating layer 22 and an adhesive insulating layer 21 in order toward one side in the thickness direction.

3.3 Third Modification Although not shown, the insulating layer 2 includes only the porous insulating layer 22 .

3.4 Fourth Modification Although not shown, the insulating layer 2 consists of an adhesive insulating layer 21 (see FIG. 1), a porous insulating layer 22, and an adhesive insulating layer 21 (see FIG. 6). Prepare side by side.

3.5 Fifth Modification One or both of the one surface and the other surface of the porous insulating layer 22 may be provided with a skin layer (not shown). The skin layer is smooth. A skin layer is a non-porous layer. When the skin layer is provided only on the other surface of the porous insulating layer 22, the insulating layer 2 consists of the adhesive insulating layer 21, the skin layer (not shown), and the porous insulating layer 22 on one side in the thickness direction. Prepare in order.

EXAMPLES Examples and comparative examples are shown below to describe the present invention more specifically. It should be noted that the present invention is by no means limited to Examples and Comparative Examples. In addition, specific numerical values such as the mixing ratio (content ratio), physical property values, and parameters used in the following description are the corresponding mixing ratios ( Content ratio), physical properties, parameters, etc. be able to.

Example 1
As shown in FIG. 4A, a laminate 6 was prepared according to the description of JP-A-2020-049905. The laminate 6 includes a second conductor layer 4 , an insulating layer 2 and an underlying conductor layer 31 . The second conductor layer 4 has a thickness of 18 μm and is made of copper. The insulating layer 2 includes an adhesive insulating layer 21 with a thickness of 20 μm and a porous insulating layer 22 with a thickness of 45 μm. The porous insulating layer 22 is made of polyimide resin, has an average pore diameter of 4.5 μm, and a porosity of 75%. The underlying conductor layer 31 has a thickness of 18 μm and is made of copper.

As shown in FIG. 4B, the laminated body 6 was irradiated with a YAG laser from one side in the thickness direction to form vias 20 in the underlying conductor layer 31 and the insulating layer 2 . The number of vias 20 was plural. The energy density of the laser in the first irradiation step was 17.2 J/cm ² or more. The energy density of the laser in the second irradiation step was 0.05 J/cm ² or more. When viewed in the thickness direction, the laser was swirled from the inside to the outside, as indicated by the arrow in FIG. 2A, within the region where the via 20 is to be formed. As shown in FIG. 3, the inner surface 25 had a tapered shape when viewed macroscopically in cross section.

Next, as shown in FIG. 4C , an additional conductor layer 32 was formed on one side of the laminate 6 in the thickness direction, and the conductive portion 5 was formed on the inner side surface 25 of the via 20 . Copper plating was performed in this step. The thickness of the additional conductor layer 32 was 6 μm. Therefore, the thickness of the first conductor layer 3 was 24 μm.

As shown in FIG. 1, a wired circuit board 1 including an insulating layer 2, a first conductor layer 3, a second conductor layer 4, and a conductive portion 5 was thereby manufactured.

Example 2, Comparative Example 2, Comparative Example 3
A printed circuit board 1 was manufactured in the same manner as in Example 1. However, as described in Table 1, the conditions of the first irradiation step were changed.

Comparative example 1
A printed circuit board 1 was manufactured in the same manner as in Example 1. However, the insulating layer 2 was provided only with a dense polyimide sheet. Also, as shown in FIG. 2B, when viewed in the thickness direction, the laser was swirled from the outside toward the inside as indicated by the arrow in FIG. 2A within the region where the via 20 is formed.

<Measurement>
Cross-sectional SEM photographs of the inner surface 25 of the wired circuit board 1 of each of Examples 1 and 2 and Comparative Examples 1 to 3 were taken, image-processed drawings were obtained, and the length L described above was measured. Table 1 shows the results. Further, FIG. 7 shows an image processing diagram of a cross-sectional SEM photograph of Example 1. As shown in FIG.

<Evaluation of Connection Reliability of Conducting Portion 5>
A thermal shock test was performed on each of the printed circuit boards 1 of Examples 1 and 2 and Comparative Examples 1 to 3 to evaluate the connection reliability of the conductive portions 5 . In the thermal shock test, the printed circuit board 1 was alternately immersed in two baths. The temperature of one liquid bath is -65°C. The temperature of the other liquid bath is 150°C. The time for immersing the printed circuit board 1 in one liquid tank was 5 minutes. A cycle of immersion in each of the two baths was performed 1,000 times.

After that, cross-sectional SEM observation was performed for each of the ten conductive portions 5 . The connection reliability of the conductive portion 5 was evaluated according to the following criteria. Table 1 shows the results.

◯: Neither one crack nor one void was confirmed from ten conductive portions 5 .
Δ: One crack or one void was confirmed.
x: Cracks and voids were confirmed, and the total number of cracks and voids was two or more.

1 Wiring circuit board 2 Insulation layer 3 First conductor layer 4 Second conductor layer 5 Conductive part 20 Via 22 Porous insulation layer 25 Inner surface 27 One surface 28 Other surface 31 Underlying conductor layer 32 Additional conductor layer C1 First connection point C2 Second connection point P1 Outermost position S Line segment

Claims (6)

an insulating layer having vias penetrating in the thickness direction;
a first conductor layer disposed on one side of the insulating layer in the thickness direction;
a second conductor layer disposed on the other side of the insulating layer in the thickness direction;
a conductive portion disposed on the inner side surface of the via and electrically connecting the first conductor layer and the second conductor layer;
A printed circuit board having a length L measured below of 1 μm or more and 10 μm or less.
Length L: In a cross-sectional view, a first connection point C1 where the one surface and the inner side surface of the insulating layer in the thickness direction are connected, and the other surface and the inner side surface of the insulating layer in the thickness direction are connected. A line segment S connecting the second connection point C2 is drawn. In a cross-sectional view, an outermost position P farthest from the line segment S is specified on the inner surface. A length L is measured as the shortest distance from the line segment S to the outermost position P. 2. The wired circuit board according to claim 1, wherein said insulating layer includes a porous insulating layer. 3. The printed circuit board according to claim 1, wherein said inner surface has a tapered shape when viewed macroscopically in cross section. A method for manufacturing the printed circuit board according to any one of claims 1 to 3,
preparing a laminate comprising a second conductor layer, an insulating layer, and a base conductor layer;
a step of irradiating the laminate with a laser from one side in the thickness direction to form vias in the underlying conductor layer and the insulating layer;
forming an additional conductor layer on the one surface of the laminate and forming a conductive portion on the inner surface of the via;
The method for manufacturing a printed circuit board, wherein the step of forming the via includes the step of irradiating laser with an energy density of 1 J/cm ² or more and 20 J/cm ² or less. 5. The printed circuit board manufacturing method according to claim 4, wherein in the step of forming the vias, the laser is rotated from the inside toward the outside in the region where the vias are formed when viewed in the thickness direction. Method. 6. The method of manufacturing a printed circuit board according to claim 4, wherein in the step of preparing the laminate, the insulating layer includes an adhesive insulating layer and a porous insulating layer in order in the thickness direction.

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